1. Field of the Invention
The present invention relates to an organic electroluminescence element used in displays and other luminescent displays of a predetermined pattern and the like, and a method of manufacturing the same.
2. Description of the Related Art
Organic electroluminescence elements are elements including at least an anode, an organic luminescent layer and a cathode on a substrate in which light emission is allowed by impressing an electric field between the electrodes to inject electrons and holes into the organic luminescent layer. Because they are self-emitting elements, displaying can be executed even though a backlight is not used as in the case of liquid crystal displays. Also, because of the simple structure, thin and light weight elements can be produced. Therefore, investigations have been actively carried out at present.
In typical constructions of the organic electroluminescence element, a transparent electrode such as ITO (Indium-Tin-Oxide) is patterned to give a desired shape on a transparent substrate such as glass, and an organic layer is formed thereon, followed by further forming a cathode thereon. The cathode and the organic materials are extremely reactive to water or oxygen, and as a consequence of occurrence of the reaction, non-light emitting spots, referred to as “dark spots” are generated. Accordingly, it was disadvantageous in that life time of the organic electroluminescence element may be shortened.
Hence, in general, a method in which water vapor, oxygen or the like is blocked by adhering a relatively thick glass processed to have a concave shape at the center thereof (hereinafter, referred to as counter bored glass) with an adhesive such as an epoxy resin such that top part of the cathode is covered, as demonstrated in Patent Document 1 has been carried out. However, according to this technique in which the counter bored glass is used, an advantage of enabling thin-modeling which is intrinsic to organic electroluminescence elements cannot be sufficiently made.
In addition, as information visual display terminals, displays having a greater size and greater number of picture elements, exhibiting a higher response speed, and being accompanied by smaller electric power consumption have been desired. To deal with these matters, it has been believed that a top emission structure, generally referred to, is essential in which the organic EL element is constructed using a thin film transistor (TFT) to provide a so called active matrix driving system, and the light is extracted from the opposite side of the TFT substrate. For attaining such a top emission structure, it was structurally impossible to extract the light from the top face when it was sealed with a metal can or a counter bored glass.
Accordingly, as set out in Patent Document 2, a method in which a polymer film with a transparent barrier film is allowed to cover on the electrode was proposed, however, when the covering is carried out by coating with a polymer film, formation of a thin film is required for improving the water vapor permeability of the polymer film itself, which may lead to increase in number of production steps. In addition, it may result in inclusion of bubbles upon attaching, and thus the element may be damaged by a slight amount of active gas in the bubble.
Additionally, a structure of sealing the organic electroluminescence element by formation with metal nitride, metal oxide or the like was proposed. Such a silicon oxide film or silicon nitride film is usually produced by a plasma CVD, sputtering method or the like. Furthermore, the protective film produced by the aforementioned method may cause film stripping due to the stress of the film itself when it is produced under a condition to permit film thickening or formation of a compact film for the purpose of improving the barrier property, and consequently the element may be broken. In order to solve the aforementioned problems, lamination of the aforementioned thin film and the organic film as suggested in Patent Document 3 was proposed. However, the process is disadvantageous in that formation of the protective film takes a long time, or it is not suited for production on a large scale because the film production cannot be perfected in single operation.
As in the foregoing, it was difficult to produce a thick film as the protective film used for improving the durability or reliability of conventionally proposed organic electroluminescence elements. Therefore, production of a pinholeless film having a high barrier property by the film alone was difficult, and further, demands for high productivity such as possible completion of forming the protective film by single film producing operation were not satisfied enough.
Accordingly, an object of the invention is to provide an organic electroluminescence element on which a protective film, which can be thickened and has a high barrier property, can be formed with high productivity, and a method of manufacturing the same.
Patent Document 1: JP-A-H5-109482
Patent Document 2: JP-A-2004-79292
Patent Document 3: JP-A-2003-17244